The research proposed has two major objectives. The first is to achieve accurate quantitative determinations of the elastic and viscous properties of blood cells and to relate these properties to the molecular constituents and ultrastructure of the membrane and cytoplasm. The second is to examine the influence of a number of pharmacologic, physiologic and pathophysiologic factors on cell deformability, ultrastructure and function. In the case of platelets, the effect of shearing flow, separately and in concert with the aforementioned factors, will receive special attention. Deformability of blood cells will be characterized not only in terms of static or quasi-static response to applied forces but also in terms of cell relaxation following sudden release of deformed cells. From relaxation data viscous properties can be deduced. This additional information is expected to reveal much more subtle changes in the structure and functional quality of cells and so facilitate detection of pathophysiologic alterations.